Patterns of dynamic irradiance affect the photosynthetic capacity and growth of dipterocarp tree seedlings

In the deeply shaded understorey of S.E. Asian rain forests the growth and survival of dipterocarp seedlings is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain in understorey plants. To test the sensitivity of photosynthesis and growth to variation in the pattern of dynamic irradiance, dipterocarp tree seedlings (Shorea leprosula and Hopea nervosa) were grown for 370 days under shaded forest light treatments of equal total daily photosynthetic photon flux density (approximately 3.3 mol m(-2) day(-1)), but characterised by either long flecks (LF) or short flecks (SF). Seedling growth was more than 4-fold greater under LF, compared with SF, in both species. Variation in the relative growth rates (RGR) and light saturated rates of photosynthesis (A(max)) were strongly positively correlated with the mean duration of sunflecks. Variation in RGR was strongly correlated with greater unit leaf rate growth, indicating that photosynthetic carbon gain per unit leaf area was greater under LF. The accumulation of starch in leaves over the diurnal period was 117% greater in both species under LF, compared with SF. Greater carbon gain in seedlings under LF is likely to have resulted from the combination of (1) greater A(max) (S. leprosula 35%, H. nervosa 40%), (2) more efficient dynamic photosynthesis, and (3) greater incident photosynthetic quantum yield, compared with seedlings receiving the SF irradiance treatment. The pattern of dynamic irradiance received by seedlings may significantly impact their growth and survival to a previously unrecognised extent, with important consequences for regeneration processes and hence forest structure and composition.     

Synthetic seed production from somatic embryos of Pinus radiata

Pinus radiata is one of the most important forestry species in the southern hemisphere. This work describes the regeneration of this plant via somatic embryogenesis from immature zygotic embryos. To improve this process, somatic embryogenic cell suspensions were established in liquid media for the generation of material for embryo maturation. Each developmental stage of these suspensions was characterized by microscopy and their growth phases quantified. An alginate-containing medium was used as an encapsulation method for the somatic embryos that were then germinated as artificial seeds in vitro. The protocols described in this work are both useful and reliable for industrial purposes.     

sse of photosynthetic parameters for the diagnosis of copper deficiency in Pinus radiata seedlings

Six-month-old water cultures of Pinus radiataI D. Don seedlings showed optimal growth, and the highest CO₂ assimilation and photosystem I-dependent ascorbate/dichlorophenolindophenol → NADP⁺ electron flow, at 3.0 uM Cu²⁺ (excess) in the hydroponic media. In the nine-month-old water cultures, when the early Cu deprivation has been overcome, the optimum for plant growth and CO₂ fixation shifts to 0.3 u M Cu²⁺ (normal); at that time, the 3.0 uM Cu²⁺ water cultures showed toxic symptoms of foliar chlorosis. Under Cu²⁺ deficient levels (0.03 uM) a clear decrease in the photosystem I-linked electron transport and CO₂ assimilation rates, as well as in the whole plant development, could be observed. Both six- and nine-month-old water cultures showed a close relationship between the Cu²⁺ concentration of the media and the foliar Cu content. However, leaf chlorophyll and the Cu content of thylakoid lamellae showed such a correlation only in the Cu²⁺ deficient and Cu²⁺ normal water cultures. The conclusion from these results is that the electron transport rate ascorbate/dicblorophenolindophenol → NADP⁺, and the Cu content of the photosynthetic membranes, can be used to diagnose a Cu deficiency in Pinus radiata plants.     

A functional-structural model for radiata pine (Pinus radiata) focusing on tree architecture and wood quality

Backgrounds and Aims

Functional–structural models are interesting tools to relate environmental and management conditions with forest growth. Their three-dimensional images can reveal important characteristics of wood used for industrial products. Like virtual laboratories, they can be used to evaluate relationships among species, sites and management, and to support silvicultural design and decision processes. Our aim was to develop a functional–structural model for radiata pine (Pinus radiata) given its economic importance in many countries.

Methods

The plant model uses the L-system language. The structure of the model is based on operational units, which obey particular rules, and execute photosynthesis, respiration and morphogenesis, according to their particular characteristics. Plant allometry is adhered to so that harmonic growth and plant development are achieved. Environmental signals for morphogenesis are used. Dynamic turnover guides the normal evolution of the tree. Monthly steps allow for detailed information of wood characteristics. The model is independent of traditional forest inventory relationships and is conceived as a mechanistic model. For model parameterization, three databases which generated new information relating to P. radiata were analysed and incorporated.

Key Results

Simulations under different and contrasting environmental and management conditions were run and statistically tested. The model was validated against forest inventory data for the same sites and times and against true crown architectural data. The performance of the model for 6-year-old trees was encouraging. Total height, diameter and lengths of growth units were adequately estimated. Branch diameters were slightly overestimated. Wood density values were not satisfactory, but the cyclical pattern and increase of growth rings were reasonably well modelled.

Conclusions

The model was able to reproduce the development and growth of the species based on mechanistic formulations. It may be valuable in assessing stand behaviour under different environmental and management conditions, assisting in decision-making with regard to management, and as a research tool to formulate hypothesis regarding forest tree growth and development.     

Leptographium terebrantis inoculation and associated crown symptoms and tree mortality in Pinus taeda

Leptographium terebrantis has been implicated as a contributing factor of P. taeda decline and mortality over the past several decades. We examined the potential of L. terebrantis to cause decline symptoms and determined the relationship between pathogen spread and the formation of new sapwood. The study was undertaken in a 13-y-old P. taeda plantation using artificial inoculations of fungal-colonized, sterilized toothpicks. We found that L. terebrantis was not only re-isolated from dying inoculated trees but caused decline symptomology and mortality at a high inoculum density. It was found that 20% mortality and severe growth loss among surviving trees occurred with L. terebrantis infection at the high density. At lower inoculum densities, trees produced a complete ring of new sapwood that appeared to sustain tree physiology. This suggests that management practices in P. taeda plantations which minimize bark beetle infestation and pathogen inoculum densities allow adequate sapwood function for sustained growth.     

Influence of pasture understoreys and tree management on soil moisture under a young New Zealand stand of Pinus radiata

Soil moisture content (SMC) and throughfall were monitored along transects between rows of radiata pine (Pinus radiata D. Don) planted at 7 m row spacing and grown with ryegrass/clover or lucerne pastures or with no understorey. SMC was recorded to 1 or 2 m depths for years 2–6 or 4–6, respectively. The predominant rainfall from the south–south–west (SSW) direction created rain shadows (60% of open pasture) on the northern sunny side of the trees. The rain shadows increased as the trees grew but their position were modified by stand pruning and thinning in years 4 and 5. SMC in the top meter showed strong positional effects with the lowest SMC under the tree crowns and on the northern side. There were strong seasonal patterns driven by high spring and summer evapotranspiration, modified by rain shadows and stand age. For the no-understorey treatment, SMC remained high midway between tree rows until the trees were 4 years old and started utilizing this moisture. For the two pasture understoreys, the difference in SMC between the north and south sides decreased with time after trees were thinned and pruned. In the no-understorey there was little difference between the two aspects. Understorey evapotranspiration and fine rooting patterns also helped explain soil moisture use patterns. No difference was detected between two contrasting radiata pine tree types. The effective rooting depth of the ryegrass/clover understorey was <0.7 m while that of lucerne and trees were deeper. Alternative tree planting practices may reduce some of the negative effects of tree-understory moisture competition.     

Relationships between tree size, crown shape, gender segregation and sex allocation in Pinus halepensis, a Mediterranean pine tree

Background and Aims

Sex allocation has been studied mainly in small herbaceous plants but much less in monoecious wind-pollinated trees. The aim of this study was to explore changes in gender segregation and sex allocation by Pinus halepensis, a Mediterranean lowland pine tree, within tree crowns and between trees differing in their size or crown shape.

Methods

The production of new male and female cones and sex allocation of biomass, nitrogen and phosphorus were studied. The relationship between branch location, its reproductive status and proxies of branch vigour was also studied.

Key Results

Small trees produced only female cones, but, as trees grew, they produced both male and female cones. Female cones were produced mainly in the upper part of the crown, and male cones in its middle and lower parts. Lateral branch density was correlated with the number of male but not female cones; lateral branches were more dense in large than in small trees and even denser in hemispherical trees. Apical branches grew faster, were thicker and their phosphorus concentration was higher than in lateral shoots. Nitrogen concentration was higher in cone-bearing apical branches than in apical vegetative branches and in lateral branches with or without cones. Allocation to male relative to female function increased with tree size as predicted by sex allocation theory.

Conclusions

The adaptive values of sex allocation and gender segregation patterns in P. halepensis, in relation to its unique life history, are demonstrated and discussed. Small trees produce only female cones that have a higher probability of being pollinated than the probability of male cones pollinating; the female-first strategy enhances population spread. Hemispherical old trees are loaded with serotinous cones that supply enough seeds for post-fire germination; thus, allocation to males is more beneficial than to females.     

The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don

Responses of photosynthesis (A) to intercellular CO₂ concentration (c_i) in 2-year-old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30°C caused a 4-fold increase in V_cmax, the maximum rate of carboxylation (10.7–43.3 μol m^?2 s^?1 and a 3-fold increase in J_max, the maximum electron transport rate (20.5–60.2 μmol m ^?2 s^?1). The temperature optimum for J_max was lower than that for V_cmax, causing a decline in the ratio J_max:V_cmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30°C. To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments. Foliar N concentrations varied between 0.36 and 1.27 mol kg^?1, and there were linear relationships between N concentration and both V_cmax and J_max. Measurements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg^?1 near the base to 1.54 mol kg^?1 near the leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.     

Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree

Sudden but transient changes in the fraction or illuminated foliage area in a well-watered 7-year-old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (g_t), stomatal conductance (g_s) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in g_t. However, when tree conductance was normalized with respect to the illuminated leaf area (g_t'), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in g_s and A up to 59 and 24%, respectively, for needles in the top third of (he crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.     

Effects of geminivirus infection and growth irradiance on the vegetative growth and photosynthetic production of Eupatorium makinoi

Eupatorium makinoi plants with or without geminivirus infection were grown in shading frames with 70, 15 and 5.5% sunlight. Growth characteristics of these plants in the early vegetative phase were compared by means of growth analysis. We also measured leaf photosynthetic gas exchange rates and examined relationships between leaf photosynthesis and whole-plant growth. Relative growth rate (RGR=(1/W)×(dW/dt), where W is plant dry mass) of virus-infected plants was lower than that of uninfected plants under all three light conditions. The reduction of RGR by infection was increased with irradiance. The net assimilation rate (NAR=(1/A)×(dW/dt), where A is total leaf area of the plant) was also reduced both by infection and shading. NARs that were estimated from light-response curves of leaf photosynthesis, in situ measurements of irradiance, and respiration rates of leaves, stems and below-ground parts, agreed very well with the values obtained by conventional growth analysis techniques. Decreases in the estimated NAR value from infection and shading were mostly explained by the decreases in leaf photosynthesis. These results clearly showed that lowered RGR in virus-infected plants was attributed mainly to impaired photosynthesis in virus-infected leaves.     

Isolation and characterization of a Pinus radiata lignin biosynthesis-related O-methyltransferase promoter

A putative promoter fragment of a Pinus radiata gene encoding a multi-functional O-methyltransferase (AEOMT) was isolated from genomic DNA. Sequence analysis revealed a number of putative cis elements, including AC-rich motifs common in promoters of genes related to the phenylpropanoid pathway. The isolated promoter was fused to the GUS reporter gene and its expression profile analyzed in transgenic tobacco and in transient transformation experiments with P. radiata embryogenic and xylogenic tissue. The promoter conferred weak expression in embryogenic tissue but caused strong GUS activity in both ray parenchyma cells and developing tracheary elements of xylem strips. Histochemical analysis in transgenic tobacco plants revealed that the AEOMT promoter induced GUS expression in cell types associated with lignification, such as developing vessels, phloem and wood fibers and xylem parenchyma as well as in non-lignifying phloem parenchyma. The isolated promoter was activated by challenge of the tissue with a fungal pathogen. Our results also indicate that the control of lignin-related gene expression is conserved and can be compared in evolutionarily distant species such as tobacco and pine.     

Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. Don tree

The three dimensional distribution of intercepted radiation, intercellular CO₂ concentration (C_i) and late summer needle nitrogen (N) concentration were determined at the tips of all 54 branches in a 6·2-m-tall Pinus radiata D. Don tree growing in a New Zealand plantation. Measurements included above- and below-canopy irradiance, leaf stable carbon isotopic composition (δ¹³C) and tree canopy architecture. The radiation absorption component of the model, MAESTRO, was tested on site and then used to determine the branch tip distribution of intercepted radiation. We hypothesized that in branch tip needles: (i) the allocation of nitrogen and other nutrients would be closely associated with the distribution of intercepted radiation, reflecting carbon gain optimization theory, and (ii) C_i would predominantly reflect changes in photosynthetic rate (A) rather than stomatal conductance (g_s), indicating that the increase in A for a given increase in N concentration was larger than the corresponding increase in g_s. Needle nitrogen concentration was poorly related to intercepted radiation, regardless of the period over which the latter was calculated. At a given height, there was a large azimuthal variation in intercepted radiation but N concentration was remarkably uniform around the tree canopy. There was, however, a linear and positive correspondence between N concentration and δ¹³C and needle height above ground (r² = 0·73 and 0·68, respectively). The very strong linear correspondence between N concentration and C_i (r² = 0·71) was interpreted, using gas exchange measurements, as supporting our second hypothesis. Recognizing the strong apical control in P. radiata and possible effects of leaf nitrogen storage in an evergreen species, we propose that the tree leader must have constituted a very strong carbon sink throughout the growing season, and that the proximity of branch tip needles to the leader affected their photosynthetic capacity and nutrient concentration, independent of intercepted radiation. This implies an integrated internal determination of resource allocation within the tree and challenges the current convention that resources are optimally distributed according to the profile of intercepted radiation.     

The influence of water stress on the photosynthetic performance and stomatal behaviour of tree seedlings subjected to variation in temperature and irradiance

Summary Seedlings of Betula pendula Roth. and Gmelina arborea L. were subjected to variation in temperature and irradiance. The influence of a mild water-stressing treatment on the photosynthetic performance and stomatal behaviour of these plants was assessed. For both species, the shape of the relationships between irradiance and photosynthesis and temperature and photosynthesis resembled those reported for other species. The effect of water stress was to reduce the rate of photosynthesis, particularly at high temperatures. This was largely a function of a reduction in mesophyll conductance under these conditions. The optimum temperature for stomatal opening was significantly lower than the optimum temperature for photosynthesis, which was in turn lowered by the water stress treatment. The stomata of birch seedlings showed maximum opening at an intermediate temperature while the stomata of Gmelina generally exhibited a closing movement when leaf temperatures increased from 15° C. Mesophyll conductances of both species increased with increasing temperature.The physiological basis for the variation in photosynthetic performance and stomatal behaviour and the ecological significance of this variation are discussed.     

Growth, Mg nutrition and photosynthetic activity in Pinus radiata: evidence that NaCl addition counteracts the impact of low Mg supply

We investigated effects of low Mg and moderately raised NaCl, as occurs in plantations irrigated with tertiary municipal effluent in New Zealand, on growth, Mg nutrition and photosynthetic activity of Pinus radiata D. Don seedlings grown in nutrient solutions with a Perlite medium. Seedlings were grown with either sufficient (0.35 mM; H[Mg]) or limited (0.033 mM; L[Mg]) Mg supply, without NaCl or with NaCl addition (8.7 mM; +[NaCl]). After 30 weeks, seedlings grown at L[Mg] displayed severe Mg deficiency symptoms, and had significantly less biomass than those at H[Mg]. While NaCl addition had an adverse effect on seedling growth at H[Mg], it increased growth at L[Mg]. The +[NaCl] treatment greatly increased the Mg uptake rates, which were associated with increased stomatal conductance and increased root to shoot ratio. Magnesium deficiency reduced the rates of light-saturated photosynthesis and stomatal conductance, but not the quantum efficiency of photosystem II, which was reduced mainly by the +[NaCl] treatment, especially at H[Mg]. Our study clearly indicated that NaCl addition could counteract the impact of low Mg supply by enhancing Mg uptake from the rooting medium.     

Environmental and nutritional responses of a Pinus radiata plantation to biosolids application

Since the mid-1990s, a Pinus radiata (D. Don) plantation growing on a sandy, low fertility soil at Rabbit Island near Nelson, New Zealand received aerobically digested liquid biosolids. An experimental research trial was established on the site to investigate the effects of biosolids applications on tree growth, nutrition, soil and ground water quality. Biosolids were applied to the trial site in 1997 and 2000, at three application rates: 0 (control), 300 (standard) and 600 kg N ha⁻¹ (high). Biosolids application significantly increased tree growth. This was mainly attributed to improved N supply, demonstrated by the enhanced N concentration in the tree foliage. Soil analysis indicated that biosolids application have not caused significant changes in concentrations of most nutrients. However, biosolids treatments significantly increased the available P (Olsen P). Of the heavy metals only total Cu concentrations in the soil increased after biosolids application. Groundwater quality, which was monitored quarterly, has not been affected by biosolids application. The concentrations of nitrate and heavy metals in groundwater were well below the maximum acceptable values in drinking water standards. Biological treatment of sewage and digestion of sewage sludge resulted in the enrichment of ¹⁵N in the biosolids (δ¹⁵N values between 5.0 and 8.7‰). Such enrichment was used as a tracer to study the fate of biosolids derived N. The elevated δ¹⁵N in biosolids treated pine foliage indicated that a considerable amount N was sourced from biosolids. Analysis of δ¹⁵N in understorey plants showed that both non-legume and legume understorey plants took up N from the biosolids, and acted as a N sink, reducing N availability for leaching. Our study showed that application of biosolids to a plantation forest can significantly improve tree nutrition and site productivity without resulting in any measurable adverse effect on the receiving environment.     

Fine Structure of Parenchymatous and Differentiated Pinus radiata Callus

The fine structure of Pinus radiata D. Don callus before andafter differentiation into stem-like tissues has been examinedwith the electron microscope. In callus prior to differentiation(here called parenchymatous callus) the cells accumulate tanninsas they age and are quite distinct from the cells of differentiatedcallus. In the latter, cambium, phloem and xylem cells may beidentified by their general morphology and by their ultrastructuralfeatures. Differentiation into a true stem-like structure is,however, incomplete in that the tissues are not uniformly oriented,and parenchyma cells of the rays and phloem contain chloroplasts.The tracheids also show unusual differentiation in that borderedpits form over their entire surface and may be of two types.The reasons for these variations are discussed.     

Effect of inbreeding on production of filled seed in Pinus radiata — experimental results and a model of gene action

Summary Pinus radiata D. Don was inbred to different degrees, commencing with a founder population of 8 clones. Yield of filled seed was determined for each mating type. Mean yields (%), relative to outcrossing, were: half-sib 102; full-sib 97; S₁ 43; S₂ 42. An epistatic model was developed to predict the empty seed yield following selfing, assuming that homozygosity for several recessive co-lethals is necessary to kill an embryo. Calculations were then extended to predict the yields following different degrees of inbreeding. The proposed model gave a better fit to present results, and to other published results of similar investigations, than did an alternative based on action of independent recessive lethals. Implications for breeding and seed production strategy are discussed.     

Competitive processes in a monoculture of Pinus radiata D. Don

Summary The changes between 9 and 40 years of age of the frequency distribution of tree diameters were studied in an experiment in a plantation of Pinus radiata D. Don in South Australia in which the spacing between trees at planting varied. Empirical functions were developed to relate tree diameter to growth rate in diameter, variance of growth rate in diameter and mortality rate. These functions were used in solving a forward diffusion equation to predict future diameter distributions. The contributions from each of the terms in the diffusion equation were examined and it was found that the drift (growth rate in diameter) term made the greatest contribution to the solution, whilst the diffusion (variance in growth rate) term had neglible effect. This implied that competition between individual trees for light was the dominant competitive process operating in this plantation, rather than below ground competition for soil resources. The ramifications of this finding to forest growth modelling are discussed.